1. Field of the Invention
The present invention relates generally to communication systems and methods, and more particularly, to reliably varying the power level of a transmitted signal, such as a transmitted radio frequency (RF) signal.
2. State of the Art
Communication systems which employ wireless transceivers are well known. However, as is the case with most electronic technologies today, there is an ever increasing demand to improve information transmission rates and range (that is, power output), while at the same time, reducing the influence of noise and improving the quality of transmission. In addition, there is always increasing demand to broaden the applicability of wireless communications to technologies still dependent on wired or fiber linked communication, such as mainframe-to-mainframe communications where high data rate and high power requirements have precluded the use of conventional wireless communications. To satisfy these competing concerns, a compromise is often reached whereby some sacrifice in transmission rate is accepted to enhance the integrity of the data transmitted. In addition, sacrifices in transmission range, and in transmitter options, such as an ability to vary the transmit power, are accepted to reduce the transceiver""s circuit complexity and cost.
An ability to adjust the power level of a transmitter output signal is desirable in conjunction with applications such as communication systems, in particular, with wireless communication systems, wherein output power requirements can change based on conditions including, but not limited to, weather conditions and distances over which wireless communication is to be performed. For example, a sunny day does not require the same transmitter power output as a rainy day. Accordingly, it would be desirable to reduce power output of the transmitter on sunny days to save power and to avoid saturation of the receiver (which results in signal distortion). Similarly, a transmission over a shorter distance permits, or can require, power output of the transmitter to be reduced. Variable output voltage attentuators are not presently available which would be suitable for the high power requirements of systems which employ high power monolithic millimeter wave integrated circuits (MMICs). Available attentuators are noisy, and are unable to provide a stable DC output which can be varied in response to an attenuator drive circuit that includes components, such as digital to analog converters.
Accordingly, it would be desirable to provide an apparatus and method for varying the power level of a transmitter output signal using a cost effective, straightforward approach that can accommodate high power requirements (e.g., 0.5 to 2 watts (W), or higher), high transmission rate systems (e.g., having operating frequencies on the order of 18-40 gigahertz (GHZ) spectrums or wider, and actual transmission rates on the order of 100 to 125 megabits per second (125 Mb/s) or higher). It would also be desirable to provide variations of the transmission power level in incremental steps which permit fine adjustment of the transmitted signal power.
The present invention is directed to an apparatus and method for varying the power level of a transmitted signal, such as a transmitted radio frequency signal, of high power, high transmission rate systems, in a relatively straightforward, cost efficient manner. Exemplary embodiments can provide a range of stable DC control voltages for driving a power level attenuator, wherein the control voltages possess essentially no AC component (e.g., in exemplary embodiments, at a 5 volt DC output, virtually no AC component in the millivolt range is present), and possess a high current capability (e.g., at a 5 volt DC output exemplary embodiments can accommodate currents in excess of 0.5 amps (A) up to 7 A or greater). The ability to provide very stable, transmission power attenuation is especially desirable for communication systems, and in particular, wireless communication systems wherein conservation of energy is important, and wherein transmission rates are on the order of 125 Mb/s or higher, and transmission power is on the order of 0.5 to 2 watts (W) or higher. Because of its high current capability, a power level attenuation controller in accordance with exemplary embodiments of the present invention is suitable for use in conjunction with high power (e.g., 0.5 W) monolithic millimeter wave integrated circuits (MMICs).
Generally speaking, exemplary embodiments of the present invention are directed to an apparatus and method for varying the power of a signal, comprising: means for receiving a regulated input voltage; means for varying said regulated input voltage to provide at least one variable control voltage having a stable voltage over a range of outputs which includes approximately 5.0 volts and a current capability of at least 0.5 amps; and means, responsive to said variable control voltage, for varying a power level of a signal to be transmitted. An exemplary apparatus for attenuating the power level of a transmitted signal includes means for converting a digital input into an analog output voltage; and means for driving a monolithic millimeter wave integrated circuit attenuator with said variable control voltage.